Which of the following substances is classified as an explosive?

The classification of a substance as an explosive is based on its ability to undergo a rapid chemical reaction that produces gas and heat, resulting in an explosion. A device designed to function by chemical reaction is typically formulated to achieve this rapid transformation, often involving a significant release of energy. This characteristic allows it to create a sudden increase in pressure and temperature, which is the fundamental aspect of an explosion.

In contrast, the other options do not meet the criteria for being explosive. A liquid with a high flashpoint is generally considered safe from igniting under normal conditions, while a poisonous gas pertains to toxicity rather than explosive capacity. A solid with a high corrosion rate refers to its reaction with moisture or other substances, predominantly causing deterioration rather than an explosive reaction. Therefore, the defining feature of the device designed to function by chemical reaction aligns directly with the criteria needed for an explosive classification.